The process by which regulatory standards are established for drinking water contaminants is based on extrapolating animal toxicity data to humans using a standard mathematical model. The assumptions and judgments involved introduce a relatively high degree of uncertainty and conservativeness into both the qualitative and quantitative aspects of the process. Setting standards based on knowledge of specific mechanisms of carcinogenicity would decrease the uncertainty involved in risk assessment. Understanding these mechanisms is necessary for arriving at the most appropriate mathematical construct for calculating more rational standards.
Small water utilities often have difficulty operating complicated treatment processes. The advanced oxidation process investigated here is simple, involving only a pump to add hydrogen peroxide and a power supply for the ultraviolet lamps, and the process does not produce any solid residuals. The results of these studies show that a photon-flux-driven pseudo-first-order model (known as the Prengle-Shimoda rate model) could be used to predict the destruction of total organic carbon, dissolved organic halogen, and dissolved organic halogen precursors.
This study investigated the control of trihalomethanes (THMs) with ion exchange by comparing the THM formation potentials of the organic fractions in the influent to three column systems. The results showed that the smallest organic fraction, <0.5 K apparent molecular weight (AMW), was most reactive with free available chlorine. With the ion exchange system, the 1--5K-, 0.5K--1K-, and < 0.5-AMW organic fractions produced the majority of THMs, whereas with the granular activated carbon (GAC) and the combined ion exchange-GAC systems, the <0.5-AMW fraction produced most of the THMs. The authors conclude that regeneration of the resin of the ion exchange column at sulfate breakthrough, in combination with a GAC column, will produce a water very low in THM formation potential.
The general approach to assessment of risk from chemical contaminants in drinking water involves three steps: hazard identification, exposure assessment, and dose-response assessment. Traditionally, the risks to humans associated with different levels of a chemical have been derived from the toxic responses observed in animals. It is becoming increasingly clear, however, that further information is needed if risks to humans are to be assessed accurately. Biologically based models help clarify the dose-response relationship and reduce uncertainty.
In the dissolved organic halogen (DOX) analytic test, prior to combustion, the granular activated carbon (GAC) on which the DOX is absorbed is washed with a sodium nitrate solution designed to remove any inorganic chloride that may have also adsorbed to the GAC. Thus, a potential positive interference is removed. This study investigated the effectiveness of the nitrate wash in eliminating possible interferences from bromide, bromate, and chlorate ions. No interference was detected from bromate or chlorate ion, but a small positive interference of about 12 micrograms Cl-/L per mg/L of bromide ion was found in the presence of background organic matter.
Colisure presence-absence medium was compared with standard reference methods for detecting low numbers of total coliform bacteria and E. coli in drinking water when the bacteria were subjected to chlorine stress. When Colisure was compared with established reference methods to detect total coliforms in dilute, disinfected samples, Colisure yielded more positive results after 24, 28, and 48 h than lauryl tryptose broth (LTB) confirmed in bile green lactose broth after 48 h. Colisure also detected higher levels of chlorine-injured E. coli than LTB confirmed in EC medium with 4-methylumbelliferyl B-D-glucuronide (EC/MUG). The sensitivity and specificity of Colisure were also evaluated and were determined to be between 96 and 100 percent on nonchlorinated samples when positive and negative tests were verified.
In order to minimize the levels of potentially toxic disinfectants and disinfection by-products in treated water while maintaining adequate protection against microbiological contamination, the total risks associated with disinfection have to be measured and compared with the risks from microbial agents. Because much work has already been carried out on chlorination and its by-products, it is recommended that research focus on major disinfection alternatives, i.e., ozonation, chloramination, carbon dioxidation, and the most practical combinations of these options. The primary research needs are (1) assessment of the relative toxicological hazards of the disinfectants and their by-products and (2) development of biologically based models for the dose-response relationships of these chemicals.
The water delivery system developed by the Romans stands as a monument to the engineering ability of that city-state's water commissioners. This is an article about that system and, in particular, one of its ablest administrators--Frontinus.
An electrochemical method for detecting bacteria, based on a linear relationship between inoculum size and the time of hydrogen evolution, was tested for the early detection and monitoring of coliforms in naturally contaminated estuarine and fresh water samples. Standard methods for coliform analysis were performed on each sample, and membrane filtration counts were used to construct dose-response curves; relationships and results are discussed herein.
The present work describes the use of an airborne electromagnetic sensing system for measuring snowpack depth, density, and water content. A transmitter sends a sequence of pulses of stepped frequencies, and the reflections are measured by a sensitive receiver. The combination of the snowpack and the earth interacts with the electromagnetic wave so as to modify the characteristics of the reflected signals. The variation of the reflected intensity with frequency provides the desired data. A theoretical analysis of return signal and snowpack parameter relationships is given, and the results of experimental verification of the theory are discussed.
Drought and dwindling supplies coupled with a growing population are severely straining California's water resources, and traditional water supply planning and analysis are proving inadequate to help the state prepare for future needs. To help ascertain the value of urban water use in California, one alternative has been the development of economic loss functions, which represent a flexible yet rigorous method to replace yield, shortage, and requirements-based approaches to assessing water supply performance for planning studies, regulatory impact assessments, and other evaluations. The approach in this article applied residential water demand elasticities for residential willingness-to-pay for water, used an industry study for industrial willingness-to-pay for water, and assumed fixed commercial sector water use for 2020 population levels. On the basis of economic loss functions described in this article, urban water scarcity in California in 2020 would cost end users an estimated average of $1.6 billion per year, given current operations, allocations, and infrastructure.
Studies were conducted to characterize the growth and composition of the schmutzdecke and the associated particle removal efficiency for a field-scale experimental slow sand filtration (SSF) system used for the biological treatment of Logan River water. A naturally occurring ammonium-selective zeolite, clinoptilolite, was added as a surface amendment to the sand bed of the SSF system as a reservoir of nitrogen for algae comprising the schmutzdecke. A predominance of filamentous algae at the surface of the filter was observed throughout the entire experimental period. The zeolite-amended SSF system treated drinking water for longer periods of time at higher filtration rates than achievable with conventional SSF without the zeolite surface amendment.
Using a Peru case study, this article examines the problem of training imbalance for water and wastewater operators. Guidelines towards achieving adequate training for all water and wastewater personnel are suggested. (Author/MA)
The practical quantitation limit (PCIL) for arsenic (As) is currently orders of magnitude higher than its nonenforceable, health-based standard in California. Analytical limitations caused by chloride (CO interference can be overcome using high-resolution, inductively coupled plasma mass spectrometry (ICP/MS), which has a method detection limit for As of 29 ng/L in the presence of 35.5 mg/L Cl. Increasing Cl concentration (0-355 mg/L) resulted in a nonlinear increase in the As signal. Therefore, standard addition was used to test four water samples with unknown As and Cl concentrations. Because standard addition is not suitable for routine analyses, further investigation of matrix effects and interferences is needed to optimize the application of high-resolution ICP/MS forwater qualitytesting. Nonetheless, broader adoption of this and other methods for trace As analysis could result in lowering of the KIL for As in the future, with consequent downward pressure on reporting levels.
Bench-scale studies were conducted in model freshwater systems to investigate how various parameters affected arsenic removal during coagulation with ferric chloride and arsenic adsorption onto preformed hydrous ferric oxide. Parameters included arsenic oxidation state and initial concentration, coagulant dosage or adsorbent concentration, pH, and the presence of co-occurring inorganic solutes. Comparison of coagulation and adsorption experiments and of experimental results with predictions based on surface complexation modeling demonstrated that adsorption is an important (though not the sole) mechanism governing arsenic removal during coagulation. Under comparable conditions, better removal was observed with arsenic(V) [As(V)] than with arsenic(III) [As(III)] in both coagulation and adsorption experiments. Below neutral pH values, As(III) removal-adsorption was significantly decreased in the presence of sulfate, whereas only a slight decrease in As(V) removal-adsorption was observed. At high pH, removal-adsorption of As(V) was increased in the presence of calcium. Removal of As(V) during coagulation with ferric chloride is both more efficient and less sensitive than that of As(III) to variations in source water composition.
Most major urban utilities or municipalities are currently aware of the need to keep records of watermains within their distribution systems. These records would typically include data such as watermain break history, pipe material, pipe vintage, soil type, etc., that would eventually be used to allocate budgets for the replacement/rehabilitation/repair of the ageing distribution system, based on objective and rational criteria. In reality, many urban utilities have incomplete or scarce relevant watermain data, which may make the financial planning task difficult. Consequently, there is a need for a methodology that facilitates the usage of scarce available data to assess the future needs of the utility to invest in the renewal of deteriorated watermains. A case study is presented in which a methodology comprising four essential steps was applied. These steps include (1) partition data on watermain breaks into homogeneous groups so that reliable predictions for future breaks could be established for regions of the water utility where available data was insufficient, (2) establish breakage rate patterns for these groups to project future breakage rates, (3) use projected breakage rates to determine the economic life of watermains, (4) examine some probabilistic scenarios of the distribution of watermain life, and (5) determine the investment required for watermain replacement. RES
Outlined are the basic elements of a strong utility employee safety program. The components discussed include: management leadership; assignment of responsibility; maintenance; establishment of safety training; accident record system; medical systems; and personal responsibility of employees. (CS)
Understanding the issues involved when multiple source waters are blended, particularly impact to distribution system water quality is important. A multi-objective technique is demonstrated that will aid in evaluating blends to identify acceptable water quality for simultaneous control of lead, copper, iron and monochloramine levels in distribution systems. Blends of three different 2 source waters (groundwater, surface water and desalinated water) are evaluated. The modeling results indicate that the different pipe materials often have conflicting water quality requirements for release abatement. Corrosion of copper and lead pipes for instance was increased by increasing alkalinity, whereas increasing alkalinity was beneficial in reducing the release of iron corrosion products from pipes. Increasing sulfates was found to reduce the release of lead, while iron release increased. These conflicting water quality requirements for lead, copper and iron release necessitate the evaluation of the tradeoffs between water quality and the corrosion response.
Development of the Canadian northland has progressed so rapidly during the last decade that the problem of providing the facilities of modern living in the North has become one of the greatest current engineering problems. Owing to unusual features of the climate and the ground, it is apparent that engineering practices of more temperature regions cannot be applied without modification. This is particularly true of the design of water and sewer services in regions of "permafrost" or perennially frozen ground. RES
Clean, safe water, a universal necessity, is not yet a universal reality. Recognizing the worldwide need for adequate water supplies and sanitation facilities, the United Nations has declared 1981-1990 the Water and Sanitation Decade. Identifying needs, planning and building satisfactory facilities, and training water supply personnel in developing nations pose a giant task. AWWA members, with an expansive range of knowledge and experience, have taken the first step in making water supply and sanitation facilities a reality for developing nations. “Water for the World—Challenge of the ‘80s” is the theme of AWWA's 1980 Annual Conference & Exposition, at which association members will begin to organize their talents and resources to meet this challenge.
For the water supply company Hydran South Holland in the Netherlands, clogged wells constituted a significant problem that lowered production capacity of the well field, disrupted the purification process at the treatment plant, and decreased overall revenues. This study was undertaken to develop a better understanding of the dogging process, the nature of the clogging materials, and the exact position of these materials in the well. The Hydron South Holland wells pump anaerobic groundwater from aquifers consisting of Pleistocene, sandy, and fluvial sediments, Samples were collected from a number of wells with a reduced specific capacity. Light microscopy and electron microscopy were performed on undisturbed samples, and particle size distribution and chemical analyses were conducted on bulk samples. On the basis of study results, a new two-pronged rehabilitation procedure was developed for seriously clogged wells. Initial findings indicate that the procedure offers both good immediate results and a significantly lower clogging rate over the long term. Hydron South Holland is conducting further research to prevent initial clogging and fine-tune well drilling techniques and well design. Utilities experiencing well clogging in similar aquifer conditions can use these findings to optimize their own rehabilitation procedures or as a jumping-off point for new research on well clogging and well design. - MPM.
Ductile iron replaced gray cast iron as pipe material in the early 1970s. It has been estimated that almost half of all new water mains installed in North America are ductile iron. The main cause of structural deterioration of all metallic mains is external corrosion, which is induced by environmental and operational conditions. Internal corrosion, on the other hand, can cause significant functional (hydraulic, water quality) deterioration within the distribution system. Methods for external corrosion protection include passive means (coatings or wraps), active means (cathodic protection), or a combination of both. Successes and failures have been reported for the use of various methods under different conditions and circumstances. This article describes the various practices used to protect ductile-iron mains from corrosion and details case histories that have been reported from around the world. The authors offer some conclusions about the suitability of the various methods to specific circumstances.
Environmental policymakers, natural resource professionals, and citizens groups are increasingly turning to a handful of collaborative processes known collectively as ‘Environmental Conflict Resolution’ (ECR) in order to reach decisions that are environmentally sound, economically feasible and politically viable. This trend is due, at least in part, to the growing realization that most natural resources are better managed at the resource level (e.g. the watershed level) rather than the level of political jurisdictions (e.g. counties, cities, water authorities). This article shares basic information about ECR processes, why and how to apply them in the context of a water utility, and ends with some successful examples of ECR’s use by water utilities.
The National Research Council Canada (NRC) recently completed a project to assist the city of Montreal, Que., in determining the condition of its water and sewer system. NRC staff members reviewed available and future diagnostic techniques for both systems; conducted experiments on corrosion monitoring, closed circuit television inspection, and mechanical inspection methods; and provided general scientific advice during the course of the project. This article describes the results of the review of diagnostic techniques for metallic and prestressed concrete pipes. Both older techniques such as water audits and leak detection and new approaches such as acoustic emission monitoring and remote-field-effect inspection are discussed. Advantages and disadvantages of each technique are tabulated, and approaches are suggested for combining the techniques to diagnose a water system completely.
Water utilities commonly use acoustic equipment to locate leaks. Although acoustic equipment is generally considered satisfactory for metallic pipes, its application to plastic pipes could be problematic. This study found that leaks in plastic pipes could be located using acoustic techniques; however, there were several difficulties. Professional leak detection teams using leak noise correlators rarely succeeded in locating leaks because the frequency range selected automatically by correlators (or manually by operators) was usually too high. The frequency content of leak signals from plastic pipes was mostly below 50 Hz. Listening devices were ineffective unless they were used very close to leaks. Acoustic leak detection methods can be made more effective by revising the automatic-mode algorithms of correlators, using finely tunable noise filters, and measuring leak signals with hydrophones or highly sensitive vibration sensors. Nonacoustic methods such as radar, thermography, and tracer gases, appear promising.
The MIEX (c) (Magnetic Ion Exchange) process, which employs an anion exchange resin for removal of dissolved organic carbon (DOC), was introduced at the Wanneroo Groundwater Treatment Plant in Western Australia in 2001. In this pilot-scale study we examined a range of operational parameters for optimisation of biofiltration of MIEX (R)-clarified waterl. Granular Activated Carbon (GAC) outperformed anthracite as a filter medium. Increasing the empty bed contact time (EBCT) from 8 to 16 minutes improved performance. The GAC biofilters removed up to 20% of DOC and up to 25% of Biodegradable Dissolved Organic Carbon (BDOC), once they had stabilised in biological mode. Chlorine demand was reduced by 51 to 55% and trihalomethane formation potential (THMFP) was reduced by 35 to 50% in GAC biofilter effluent waters at 16 minutes EBCT when compared with their MIEX (R)-treated influent water. GAC biofilters developed more biomass on the surface than anthracite biofilters and this was associated with the greatest BDOC and DOC removals. Interestingly, neither biofilters developed populations of protozoans. Use of chlorinated influent water severely restricted biomass development in all biofilters at surface. Biofilter treatment of chlorinated influent water resulted in the poorest removal of Assimilable Organic Carbon (AOC). Biofiltration improved the water quality of MIEX (R)-clarified waters.
A survey of 27 slow sand filtration plants in the United States indicated that most of these plants are currently serving communities of fewer than 10 000 persons, are more than 50 years old, and are effective and inexpensive to operate. A slow sand filtration research facility in Logan, Utah, was compared with the operating plants to determine if locally available, unsieved sand achieved similar results. The 75-m²/d research facility performed well in removing turbidity, coliform bacteria, and particles of a size representative of Giardia cysts. Una encuesta de 27 plantas de filtración lenta por arena en los Estados Unidos indicó que la mayor parte de estas plantas actualmente sirven a comunidades de menos de 10 000 personas, tienen más de 50 años, y que son efectivas y se operan a bajo costo. Una facilidad de investigación de filtración lenta por arena en Logan, Utah, fue comparada con plantas en operación para determinar si la arena sin cernir disponible localmente lograba resultados similares. La facilidad de investigación de 75-m³/d Ilenó bien su requisito de remover turbidez, bacterias coliformes y partículas de un tamaño equivalente a los quistes de Giardia.
Despite red water being one of the largest consumer water quality complaint categories, none of the models available to date can adequately address iron release in drinking water distribution systems. This is due to the complex nature of iron sources, iron release mechanisms, often conflicting impacts of various physio-chemical and biological factors, pipe material and age and the cocktails of corrosion products released. This paper presents a mathematical and pilot-scale empirical development and quantification of a unique zero-order Flux model. Iron concentration was found to depend on surface release flux (Km), pipe material, pipe geometry and hydraulic retention time. Flux is a function of pipe material, water chemistry and Reynolds Number. In the galvanized iron, Km (mg Fe/m2-d) has values of 1.99 and 0.0045(Re -2000) + 1.99 under laminar and turbulent flow conditions, respectively. Similarly, Km was found to be 4.16 and 0.009(Re ? 2000) + 4.16 for unlined cast iron pipe under laminar and turbulent flow conditions respectively.
Summarized are current analytical techniques used to classify, isolate, resolve, identify, and quantify organic compounds present in drinking water. A variety of methods are described, then drawbacks and advantages are listed, and research needs and future trends are noted. (CS)
The variation of the temperature of the soil, throughout the year and at different depths below ground surface, might seem to be a scientific curiosity of little practical interest to the water works engineer until the relation of soil temperature to the freezing of water pipes is appreciated. The freezing of water in buried mains is due, largely, to the cooling of the surrounding soil below the freezing point of water. This cooling is but one particular feature of a general pattern of the changing soil temperature profile as the effect of winter air temperatures is felt beneath the surface of the ground. RES
Various problems associated with water resources after the tsunami disaster are discussed. In regions such as Indonesia, Thailand, Sri Lanka, and India, water and sanitation system were destroyed, and seawater has contaminated supplies deep inland. The immediate loss of life due to the tsunami will be outstripped by the number of people dying from drinking unsafe water under ordinary circumstances. It is hoped that the tsunami disaster will generate greater public and governmental awareness of safe water and sanitation concerns not only in Asia but throughout the world.
Every so often, solitary voices in the past proclaimed a need to do something about the environment. Until the last few years, however, environmental-system analysis was disdained because the environment was not considered important enough by those who made policy. The authors report on the procedures that are being used now that the situation has changed.
In his monthly column, AWWA Executive Director Jack Hoffbuhr discusses the importance of the value of water as opposed to the cost of water. He stresses the myriad benefits we receive from water such as the value of being healthy so we can be productive, the value of a consistent supply of safe water, and the worth of a village and lives made possible by safe drinking water. He states that instead of focusing on costs of supplying water and water rates, it would be more beneficial to stress the value and the multitude of benefits we receive from water.
For the manager or supervisor who is not oriented to data processing, the author discusses the need and functions of the computer as a management tool. The Denver Water Dept. is developing a management-information system, described by the author, in order to provide additional and more meaningful information and to gain use of improved communications techniques.
Trying to imagine today's information technology would have been impossible 50 years ago, and it is even more challenging to predict the next 50 years. One thing is clear, although there will be changes in technology, there will be even bigger changes in how people use it. Human interaction with technology will become a paramount issue as technology becomes more integrated into the society. Utilities and utility managers in the twenty-first century will need a greater understanding of how to use and control business technology so that technology does not control them.
This article discusses the prospects for securing a sufficient energy supply, without which it will be impossible to provide an adequate water supply for Southern California, and the possible costs of a water supply.